This invention relates to pacing leads that are implantable in the body and is more particularly concerned with a stylet for use with such pacing leads with a view to stiffening them during implantation.
Implantable pacing leads are nowadays widely used in medicine for making diagnoses, for treating patients and particularly for providing cardiacs with pacemakers.
These pacing leads comprise a hollow elongated electric conductor that is highly flexible and which is sheathed with insulating material over its entire length. The conductor as such usually consists of a helical winding of several strands of wire, the strands being also helicoidally wound. Such a construction provides the conductor with the required flexibility for it continuously to adapt to the changes in shape of the blood vessels through which it extends, in particular in the region of the heart. For implantation, however, the conductor should be sufficiently rigid for the pacing lead to be inserted in the blood vessels and it is one of the functions of a stylet temporarily to provide the conductor with the required stiffness. Such a stylet may comprise a stiffish filament of elastic metal that is inserted into the pacing lead conductor and that is somewhat longer than the latter.
Once the assembly of the pacing lead and the stylet is implanted by a surgeon, he then withdraws the latter and connects the distal end of the pacing lead conductor to a pacemaker or similar device.
As is known, a pacing lead, particularly a pacing lead used to pace the heart, must become fastened to the tissue having to be stimulated and this is generally achieved by providing the operative member or electrode of the pacing lead with a suitably shaped head for example by means of a particular configuration of its surface or by barbs inclined to the longitudinal axis of the pacing lead. Despite these precautions, the pacing electrode still frequently comes loose, particularly during the first few weeks after implantation as the tissue has not yet been able to grow sufficiently to latch on to the electrode to keep the pacing lead in place. Surgeons thus regularly check whether the pacing lead has fastened properly some time after implanting it. This checking operation may be performed with a stylet similar to that used for the implantation.
An implanted pacing lead normally closely follows the sinuosities of the blood vessels in which it is inserted. At time, however, it may become quite convoluted after the stylet is withdrawn, particularly where the blood vessel branches off. The conductor of the pacing lead may then, for instance, form single or even double, e.g. S-shaped, twists or bends. Now, if the stylet filament is fitted with a simple blunting tip such as a ball point (such as disclosed in UK Patent Application No 2, 064, 963) or even more simply is formed with a rounded nose (such as dislosed in U.S. Pat. No. 2,118,631), the stylet can then only be inserted with difficulty into the conductor as the tip or nose tends to catch in the grooves between the contiguous turns of the conductor. In so doing, the tip or nose will tend to move them apart and even to be pushed through the conductor and the insulating sheath surrounding it. If this happens, the stylet is then very likely to perforate the blood vessel. This has induced practitioners to discard this method of checking the implantation of pacing leads and to resort to X-rays instead.